The invention concerns a process for denoxification of off-gases from annealing and pickling lines, wherein the off-gases from the pickling section are heated and denoxified by selective catalytic reduction (SCR), and an annealing and pickling line, especially for stainless steel hot or cold strip, comprising at least one annealing furnace and at least one pickling section, as well as a plant for selective catalytic reduction which is connected to the off-gas system of at least one pickling section.
Conventional combustion plants have used selective catalytic reduction (SCR) technology to denoxify fumes for quite some time. In this process, nitrogen oxides (NOx) are converted to nitrogen and water with the help of a catalyst. This technology is also used in the treatment of NOx-containing off-gases in the chemical processing of metals, especially in pickling processes.
SCR catalysts typically require operating temperatures between 250° C. and 300° C. to develop sufficient activity. The lowest operating temperature would be around 200° C., the limiting factor being the formation of ammonium nitrate. As the off-gases from the pickling lines are discharged at approximately 40° C., heating these off-gases to the temperatures required for SCR calls for high expenditure.
Metal processing lines separated from the pickling section often have annealing furnaces equipped with low-NOx burners. The NOx content to be guaranteed for the furnace off-gases, 200 to 240 mg/Nm3, is difficult to meet with some operating modes, so that additional expenditure is required if the guaranteed values are to be met safely.